1. The Field of the Invention
The present invention relates generally to supported catalysts and methods for making and using such catalysts (e.g., in the direct synthesis of hydrogen peroxide). The support material is functionalized with a mineral acid (e.g., concentrated sulfuric acid) or a derivative thereof to improve the bonding of the catalyst to the support.
2. The Related Technology
Hydrogen peroxide is a commercially important product which is widely used in the textile industry, paper industry, and chemical industry as a bleaching agent, biocide, and chemical reagent. Traditionally, hydrogen peroxide has been manufactured through a process which includes multiple oxidation and reduction steps using alkylanthraquinones. This process is complicated and expensive because of the many steps involved, the large volumes of reagents, the relatively high cost of intermediates, and the production of inactive by-products.
Recently, efforts have been made to develop an alternative process whereby hydrogen peroxide is directly synthesized from hydrogen and oxygen using precious metal catalysts. The direct synthesis of hydrogen peroxide offers significant economic advantages because it avoids making intermediate products and does not need the use of reagents such as alkylanthraquinones.
One important aspect of a direct synthesis process is the catalyst, which must be able to selectively convert hydrogen and oxygen to hydrogen peroxide, with minimal production of water, a competing by-product that is thermodynamically favored over hydrogen peroxide. In general, catalysts for the direct synthesis reaction use palladium or a combination of palladium and platinum, as the active catalyst. These catalysts are generally used in the form of small particles dispersed on a solid catalyst support.
While catalysts formed from small particulates can advantageously have high activity, small particulates present a problem with attrition. Because of the high cost of the active catalyst metals, the metals need to be used efficiently and should be recoverable. In some cases, metal that separates from the support can be recovered in expensive filtration systems. However, many of the metal particles that separate from the support are too fine to be recovered in the filtration process and are thus unrecoverable. Modifying the support and/or the catalyst particles to reduce attrition is very difficult because the task must be accomplished without significantly effecting catalyst performance.